1. Field of the Invention
The present invention relates to an underbody structure of a vehicle including a pair of left and right rear frames located at the rear of a floor panel, the left and right rear frames being separated from each other by a specific distance across the vehicle with a fuel tank disposed between the two rear frames.
2. Description of the Related Art
FIG. 16 shows a typical example of an underbody structure conventionally employed in a vehicle.
Referring to FIG. 16, the conventional underbody structure of includes a rear floor 102 which is connected a floor panel 100 via a kick-up part 101 formed by raising a rear portion of the floor panel 100. The underbody structure further includes a rear cross member 103 installed at the rear of an upper portion of the kick-up part 101 under a forward portion of the rear floor 102, the rear cross member 103 extending widthwise across the vehicle. A fuel tank 104 is installed at the rear of the rear cross member 103 and a rear seat 105 is mounted above the rear floor 102.
While the rear cross member 103 serves to enhance the stiffness of the vehicle body and to protect the fuel tank 104 from a side impact load, the rear cross member 103 is installed at an undesirable location from a viewpoint of seating comfort and the capacity of the fuel tank 104 in the conventional underbody structure.
Generally, there are sometimes conflicting requirements in vehicle design. One of these requirements is to make adequate leg space available for rear-seat passengers by installing the rear seat 105 and the kick-up part 101 at as rear a location as possible, providing thereby improved ride comfort, and another is to make the capacity of the fuel tank 104 as large as possible. It is necessary to position the kick-up part 101 at as rear a location as possible for providing improved ride comfort. On the other hand, it is necessary to extend the fuel tank 104 frontward for increasing the capacity of the fuel tank 104. Therefore, a vehicle body structure must generally be designed by taking different approaches to meet these conflicting requirements at the same time. If the vehicle must have a compact body, there arises an additional requirement that the amount of any overhang in a rear part of the vehicle must be made small. It is difficult to meet this requirement, however, if the rear cross member 103 is located at the rear of the upper portion of the kick-up part 101 as shown in FIG. 16.
Japanese Unexamined Patent Publication No. 1993-50952 discloses an arrangement in which a rear cross member is provided on an upper portion of a rear side of a kick-up part, and a fuel tank is located between left and right rear side frames which are provided at the rear of the rear cross member. If the rear cross member is located at the front of the fuel tank, however, there arises a problem that the presence of the rear cross member makes it difficult to provide improved ride comfort and increase the capacity of the fuel tank as in the structure of FIG. 16.
Also, Japanese Laid-open Utility Model Publication No. 1993-71083 proposes an arrangement in which a fuel tank is located at a kick-up part. The arrangement of this prior art Publication is not intended to provide improved ride comfort and increase the capacity of the fuel tank, however.
Furthermore, Japanese Unexamined Patent Publication No. 1993-155258 shows an arrangement in which a fuel tank is formed to fit the shape of a rear side of a kick-up part and mounted immediately along the rear side of the kick-up part. This approach however has a problem that the proposed fuel tank design is too complicated and unfeasible from a viewpoint of practical application.